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Fixed a snappy compression wrapper bug (passing wrong variable).
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Change atomic_pointer.h to prefer a memory barrier based
implementation over a <cstdatomic> based implementation for
the following reasons:
(1) On a x86-32-bit gcc-4.4 build, <ctdatomic> was corrupting
    the AtomicPointer.
(2) On a x86-64-bit gcc build, a <ctstdatomic> based acquire-load
    takes ~15ns as opposed to the ~1ns for a memory-barrier
    based implementation.

Fixes issue 9 (corruption_test fails)
http://code.google.com/p/leveldb/issues/detail?id=9

Fixes issue 16 (CorruptionTest.MissingDescriptor fails)
http://code.google.com/p/leveldb/issues/detail?id=16



git-svn-id: https://leveldb.googlecode.com/svn/trunk@36 62dab493-f737-651d-591e-8d6aee1b9529
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[email protected] committed Jun 30, 2011
1 parent 85f0ab1 commit ed154f6
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208 changes: 65 additions & 143 deletions port/atomic_pointer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -4,210 +4,132 @@

// AtomicPointer provides storage for a lock-free pointer.
// Platform-dependent implementation of AtomicPointer:
// - If the platform provides a cheap barrier, we use it with raw pointers
// - If cstdatomic is present (on newer versions of gcc, it is), we use
// a cstdatomic-based AtomicPointer
// - If it is not, we define processor-dependent AtomicWord operations,
// and then use them to build AtomicPointer
//
// a cstdatomic-based AtomicPointer. However we prefer the memory
// barrier based version, because at least on a gcc 4.4 32-bit build
// on linux, we have encountered a buggy <cstdatomic>
// implementation. Also, some <cstdatomic> implementations are much
// slower than a memory-barrier based implementation (~16ns for
// <cstdatomic> based acquire-load vs. ~1ns for a barrier based
// acquire-load).
// This code is based on atomicops-internals-* in Google's perftools:
// http://code.google.com/p/google-perftools/source/browse/#svn%2Ftrunk%2Fsrc%2Fbase

#ifndef PORT_ATOMIC_POINTER_H_
#define PORT_ATOMIC_POINTER_H_

#include <stdint.h>
#ifdef LEVELDB_CSTDATOMIC_PRESENT

///////////////////////////////////////////////////////////////////////////////
// WE HAVE <cstdatomic>
// Use a <cstdatomic>-based AtomicPointer

#include <cstdatomic>
#include <stdint.h>

namespace leveldb {
namespace port {

// Storage for a lock-free pointer
class AtomicPointer {
private:
std::atomic<void*> rep_;
public:
AtomicPointer() { }
explicit AtomicPointer(void* v) : rep_(v) { }
inline void* Acquire_Load() const {
return rep_.load(std::memory_order_acquire);
}
inline void Release_Store(void* v) {
rep_.store(v, std::memory_order_release);
}
inline void* NoBarrier_Load() const {
return rep_.load(std::memory_order_relaxed);
}
inline void NoBarrier_Store(void* v) {
rep_.store(v, std::memory_order_relaxed);
}
};

} // namespace leveldb::port
} // namespace leveldb

#else
///////////////////////////////////////////////////////////////////////////////
// NO <cstdatomic>
// The entire rest of this file covers that case
#endif
#ifdef OS_WIN
#include <windows.h>
#endif
#ifdef OS_MACOSX
#include <libkern/OSAtomic.h>
#endif

#if defined(_M_X64) || defined(__x86_64__)
#define ARCH_CPU_X86_FAMILY 1
#elif defined(_M_IX86) || defined(__i386__) || defined(__i386)
#define ARCH_CPU_X86_FAMILY 1
#elif defined(__ARMEL__)
#define ARCH_CPU_ARM_FAMILY 1
#else
#warning Please add support for your architecture in atomicpointer.h
#endif

namespace leveldb {
namespace port {
namespace internal {

// AtomicWord is a machine-sized pointer.
typedef intptr_t AtomicWord;

} // namespace leveldb::port::internal
} // namespace leveldb::port
} // namespace leveldb

// Include our platform specific implementation.
///////////////////////////////////////////////////////////////////////////////
// Define MemoryBarrier() if available
// Windows on x86
#if defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY)

// void MemoryBarrier(void) macro is defined in windows.h:
// windows.h already provides a MemoryBarrier(void) macro
// http://msdn.microsoft.com/en-us/library/ms684208(v=vs.85).aspx
// Including windows.h here; MemoryBarrier() gets used below.
#include <windows.h>

///////////////////////////////////////////////////////////////////////////////
// Mac OS on x86
#elif defined(OS_MACOSX) && defined(ARCH_CPU_X86_FAMILY)

#include <libkern/OSAtomic.h>

namespace leveldb {
namespace port {
namespace internal {
#define LEVELDB_HAVE_MEMORY_BARRIER

// Gcc on x86
#elif defined(__GNUC__) && defined(ARCH_CPU_X86_FAMILY)
inline void MemoryBarrier() {
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
// See http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html for a discussion on
// this idiom. Also see http://en.wikipedia.org/wiki/Memory_ordering.
__asm__ __volatile__("" : : : "memory");
#else
OSMemoryBarrier();
#endif
}
#define LEVELDB_HAVE_MEMORY_BARRIER

} // namespace leveldb::port::internal
} // namespace leveldb::port
} // namespace leveldb

///////////////////////////////////////////////////////////////////////////////
// Any x86 CPU
#elif defined(ARCH_CPU_X86_FAMILY)

namespace leveldb {
namespace port {
namespace internal {

// Mac OS
#elif defined(OS_MACOSX)
inline void MemoryBarrier() {
__asm__ __volatile__("" : : : "memory");
OSMemoryBarrier();
}
#define LEVELDB_HAVE_MEMORY_BARRIER

} // namespace leveldb::port::internal
} // namespace leveldb::port
} // namespace leveldb

#undef ATOMICOPS_COMPILER_BARRIER

///////////////////////////////////////////////////////////////////////////////
// ARM
#elif defined(ARCH_CPU_ARM_FAMILY)

namespace leveldb {
namespace port {
namespace internal {

typedef void (*LinuxKernelMemoryBarrierFunc)(void);
LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
(LinuxKernelMemoryBarrierFunc) 0xffff0fa0;

inline void MemoryBarrier() {
pLinuxKernelMemoryBarrier();
}
#define LEVELDB_HAVE_MEMORY_BARRIER

} // namespace leveldb::port::internal
} // namespace leveldb::port
} // namespace leveldb

#else
#error "Atomic operations are not supported on your platform"
#endif

///////////////////////////////////////////////////////////////////////////////
// Implementation of AtomicPointer based on MemoryBarriers above

namespace leveldb {
namespace port {
namespace internal {

// Atomic operations using per-system MemoryBarrier()s

inline AtomicWord Acquire_Load(volatile const AtomicWord* ptr) {
AtomicWord value = *ptr;
MemoryBarrier();
return value;
}

inline void Release_Store(volatile AtomicWord* ptr, AtomicWord value) {
MemoryBarrier();
*ptr = value;
}

inline AtomicWord NoBarrier_Load(volatile const AtomicWord* ptr) {
return *ptr;
}

inline void NoBarrier_Store(volatile AtomicWord* ptr, AtomicWord value) {
*ptr = value;
}

} // namespace leveldb::port::internal
// AtomicPointer built using platform-specific MemoryBarrier()
#if defined(LEVELDB_HAVE_MEMORY_BARRIER)
class AtomicPointer {
private:
void* rep_;
public:
AtomicPointer() { }
explicit AtomicPointer(void* p) : rep_(p) {}
inline void* NoBarrier_Load() const { return rep_; }
inline void NoBarrier_Store(void* v) { rep_ = v; }
inline void* Acquire_Load() const {
void* result = rep_;
MemoryBarrier();
return result;
}
inline void Release_Store(void* v) {
MemoryBarrier();
rep_ = v;
}
};

// AtomicPointer definition for systems without <cstdatomic>.
// AtomicPointer based on <cstdatomic>
#elif defined(LEVELDB_CSTDATOMIC_PRESENT)
class AtomicPointer {
private:
typedef internal::AtomicWord Rep;
Rep rep_;
std::atomic<void*> rep_;
public:
AtomicPointer() { }
explicit AtomicPointer(void* p) : rep_(reinterpret_cast<Rep>(p)) {}
explicit AtomicPointer(void* v) : rep_(v) { }
inline void* Acquire_Load() const {
return reinterpret_cast<void*>(internal::Acquire_Load(&rep_));
return rep_.load(std::memory_order_acquire);
}
inline void Release_Store(void* v) {
internal::Release_Store(&rep_, reinterpret_cast<Rep>(v));
rep_.store(v, std::memory_order_release);
}
inline void* NoBarrier_Load() const {
return reinterpret_cast<void*>(internal::NoBarrier_Load(&rep_));
return rep_.load(std::memory_order_relaxed);
}
inline void NoBarrier_Store(void* v) {
internal::NoBarrier_Store(&rep_, reinterpret_cast<Rep>(v));
rep_.store(v, std::memory_order_relaxed);
}
};

// We have neither MemoryBarrier(), nor <cstdatomic>
#else
#error Please implement AtomicPointer for this platform.

#endif

#undef LEVELDB_HAVE_MEMORY_BARRIER
#undef ARCH_CPU_X86_FAMILY
#undef ARCH_CPU_ARM_FAMILY

} // namespace leveldb::port
} // namespace leveldb

#endif // LEVELDB_CSTDATOMIC_PRESENT

#endif // PORT_ATOMIC_POINTER_H_
2 changes: 1 addition & 1 deletion port/port_posix.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@ inline bool Snappy_Uncompress(const char* input_data, size_t input_length,
::std::string* output) {
#ifdef SNAPPY
size_t ulength;
if (!snappy::GetUncompressedLength(input_data, ulength, &ulength)) {
if (!snappy::GetUncompressedLength(input_data, input_length, &ulength)) {
return false;
}
output->resize(ulength);
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